Hydraulic shafts are frequently used to propel the raising and lowering elements of a supporting structure. These devices are well known and are used in the transportation field, as well as in construction and other areas requiring frequent raising and lowering of loads that are too heavy for people to lift.
The conventional way of maintaining the charge on a shaft is to use an anti-return valve inserted in the valve supply circuit opening in the direction of the shaft outlet chamber. Maintaining the charge in this way ensures that the device operates properly so long as the valve remains sealed. This is a quality control feature incorporated during the manufacturing process. However, the valve may either gradually or suddenly fail to seal after a certain period of time for various reasons connected to its operation, or due to aging or even a minor undetected structural defect. One possible cause could be a structural defect such as a ball bearing that is not perfectly spherical, or a solid impurity from the oil circuit lodging in the valve, or some other source of faulty mechanical contact or irregular thickening between the valve body and its socket.
Such defects cause leaks which, even if insignificant, slowly weaken the charge after a period of hours, posing a danger to both the material and to the people working beneath the mechanism.
Thus, it is imperative to maintain this charge in all applications where holding the shaft securely in the supporting position is an important and primary safety concern.
In the case of hydraulic shafts, the only way to guaranty that an anti-return valve maintains its charge on the shaft is to be certain the valve is sealed.
To prevent failure in a function as important as cylinder maintenance, the valve must be completely sealed.
Presently, there is no such guaranty, and for this reason, when safety requires it, lifting cylinders are associated with blocking-locking mechanical devices, for example, locking pins or safety stops.
The goal of such blocking-locking devices or stops is to ensure that the charged support structures remain in position if there is a prolonged mechanical malfunction. Although maintaining the structures securely in position is a safety measure for the benefit of both the merchandise and the people operating the shaft and the control circuit, it has not be possible to ensure complete safety because there is always a possibility of leaks in the anti-return valve.